Recently, MPLS has received a lot of attention as packet transmission technology. The IETF (Internet Engineering Task Force) is promoting specification study and standardization of PWE3 (Pseudo Wire Emulation Edge-to-Edge), which provides existing services (such as FR (Frame Relay), ATM, TDM, and Ethernet) on an end-to-end (point-to-point) basis utilizing MPLS as tunneling technology. From the standpoint of service integration, Pseudo Wire (PW) technology utilizing MPLS is expected to expand into carrier networks and will require further higher reliability in the future.
FIG. 1 illustrates a model diagram of PWE3 defined by IETF (RFC (Request For Comments) 3915, 3986). FIG. 1 illustrates a PSN (Packet Switched Network) 1 in which a PSN tunnel 2 and Pseudo Wire PW are established between provider edges PE1 and PE2. In the Pseudo Wire PW, PW1 and PW2 are established in correspondence with customer services, for example. The provider edge PE1 is connected to a customer edge CE1 outside the Pseudo Wire PW via an attachment circuit 3, and the provider edge PE2 is similarly connected to a customer edge CE2 outside the Pseudo Wire PW via an attachment circuit 4.
Here, an end-to-end service 5 (such as Ethernet, ATM, Frame Relay, TDM, and PPP/HDLC) is emulated using a packet network. As technology which provides virtual pipes (tunnels), MPLS and L2TP (Layer 2 Tunneling Protocol) are mainly used.
In carrier networks, high reliability must be ensured. As an example, it is important to construct efficiency-focused connection management technology, and a mechanism in which for example a single failure in a network does not become a load on end users is required.
ITU-T Recommendation Y.1731, which specifies carrier Ethernet OAM (Operation, Administration, and Maintenance) has realized a mechanism considering the above. The specific configuration is illustrated in FIGS. 2A, 2B, and 2C. In the Ethernet service illustrated in FIGS. 2A and 2B (i.e., a service to aggregate traffic between CE1-[1, 2, . . . , n] CE2-[1, 2, . . . , n] at PE1 and PE2), Y.1731 specifies that a provider layer OAM management domain be provided in a provider domain PE1-PE2, and also that a customer layer OAM management domain be provided in a CE domain, and this customer domain is set in a manner that overlays the provider domain. FIG. 2B illustrates a case in which this system has a hierarchical structure including a customer layer 21 and a provider layer 22.
In this case, alarm forwarding when a single failure occurs in the provider management domain 22 between PE1-PE2 is performed in a manner such that an apparatus at the failure end generates an AIS (Alarm Indication Signal), detects LOC (Loss of Continuity), and notifies PE1 and PE2 of the AIS. Receiving this notice triggers PE1 and PE2 to generate an AIS notice for the customer domain and deliver it to the end point. On receiving the AIS, an alarm inhibit function operates to inhibit LOC detection, and at the same time a failure in the service domain may be detected and recognized.
FIG. 2C illustrates a case in which there is no hierarchical structure. While a failure in the service domain may be detected by not receiving a CC (Connectivity Check) transmitted from the customer device, receiving no CC may be detected in principle with a time-out of a timer having a length several times longer than a transmission interval. Therefore the detection time is estimated to be much longer than that in FIG. 2B. While reducing the detection time may be achieved by speeding up (shortening) the CC cycle, in that case, not only might bandwidth in the provider be suppressed, but also processing at PEs may be burdened with a load.
As described above, layer management in a packet network is important to achieving flexible connection management for each customer. Considering the above, it is necessary to construct layers such those as illustrated in FIG. 3 in PW/MPLS also, and based on that, a mechanism for providing OAM, connection management, and failure notification is required. Specifically, the service layer 31 corresponds to the customer layer 21, and the Pseudo Wire (PW) layer 32 and the MPLS layers 33 and 34 correspond to the provider layer 22. Packets consisting of L2 and OAM (FDI, etc.), and packets consisting of L1, P1, and OAM (BDI, etc.) are bidirectionally transmitted from PE2 to PE1, and from PE1 to PE2, respectively. When a failure is reported/detected in the MPLS layer 34, escalation to the PW layer 32 and the service layer 31 is required. In other words, since each layer is independent of the others, it is necessary to perform LOC detection by timing out for each PW unit at PE1. Even in the case of a failure in the MPLS LSP (Label Switching Path), there is no mechanism to notify the PW layer 32 of an alarm, and as a result, a failure is detected by Loss Detection (timer-dependent) which may be not only time-consuming, but also complicated since one-to-one processing is performed for each PW.
In addition, it is necessary to insert flags equivalent to RDI (Remote Defect Indication) on the opposite part. Unlike what is illustrated in FIGS. 2B and 2C, the MPLS layers 33 and 34 existing under the PW layer 32 have two unidirectional paths. Therefore it is necessary to assume a unidirectional failure and thus that RDI is a necessary function. Consequently, this optional function to insert the RDI is further required. In the MPLS layers 33 and 34, communication is performed through tunnels 35 and 36.
Considering the above, processing for each PW becomes complicated as in FIG. 2B in the PW/MPLS above. And as was described in the beginning, it is desirable that PE1 be notified of a failure on the basis of a single failure occurring below the MPLS layer, and then RDI may be generated. However, this has not been achieved satisfactorily with the current framework. Specifically, escalation to the PW layer 32 and the service layer 31 cannot be achieved when a failure is notified/detected in the MPLS layers 33 and 34.
This situation is illustrated more specifically in FIG. 4. OAM, which is equivalent to AIS occurring in a lower layer of PW (ITU-T Y.1711 FDI, for example), is received at PE1. PE1 needs to extract labels P1-1˜P1-n to identify opposite customer services with L2 or LSP2 (MPLS label) to identify this AIS equivalent OAM.
However, the current framework of signaling (label distribution) is independent for each layer (MPLS, PW). Practically, RSVP-TE defined in RFC3209 or LDP (Label Distribution Protocol) defined in RFC3036 are used in MPLS, and LDP defined in RFC4447 (RFC3036) is used in PW. These are performed in independent procedures based on IP (Internet Protocol). In other words, there is a possibility that a signal for signaling or a label mapping message may not be transmitted on the MPLS tunnel in a configuration of PW, and thus the opposite labels of the tunnel-directed label L2 or the customer service identification labels P1-1˜P1-n may not be extracted.
While patent document 1 discloses alarm forwarding in a network, it is different from embodiments of the present invention in that a wavelength is used in a unidirectional link.    Patent Document 1: Japanese Laid-open Patent Publication No. 2004-312152